最新牙科放射线学(2)291【共享精品-】幻灯片.ppt

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1、牙科放射线学(2)291【共享精品-】ReferencesforthepresentlectureHistoricalperspectiveCTscannercomponentsGenerationsofCTmachineCTnumberWindowlevelandwidthUseofcontrastmedium學習目標Referencesforthepresentlecture1.沈茂忠etal,電腦斷層攝影診斷學,3rdedition,Chapter1,p.1-183.HoferM,CTteachingmanual,1stedit

2、ion,p.1-132001,November2.BasicPrinciplesofComputedTomography,EdwinT.Parks,P.547-567Translate-rotatescannerSecond–generationmachineCanaccommodatethewholebodyScantimeforasingleslice:20secondThesecondscanner:drawbackLineararrangementofdetectors:Detectorsinthemiddleofarrayw

3、ereadifferentdistancefromtheradiationsourcethanthoseattheendsIncreasethescatterradiationanddegradetheimagequality第二代gantry與第一代gantry不同處乃detectors增多X光源為扇形，且旋轉角度加大(構成一圖像需18次橫移)Ref.1DetectorsGantryGantryApertureXraytubeThird-generationCT-scannerX-raysourceFanbeamDetectora

4、rray(Curved)Ref.2Rotate-rotatescannerThird–generationmachineCanaccommodatethewholebodyScantimeforasingleslice:onesecondThethirdscanner:Contain30detectorsandcoverbetween30o~60owithasingleprojectionRef.1X-raytubeCurveddetectorssolvethedifferentialmagnificationproblemofl

5、ineardetectorsRingartifact-ifasingledetectorinthearraywasdefective第三代gantry只須做旋轉式的移動，不須做橫的移動，且detectors也增多，因此構圖速度更快DetectorsGantryGantryApertureXraytubeRotate-onlyscannerFourth–generationmachineCanaccommodatethewholebodyScantimeforasingleslice:

6、:Detectorarrayconsistedofseveralthousandelements&provided360oofcoverage–avoidtheringartifactPatient‘sradiationdoseisincreasedDetectors360o排滿了gantry之四周，且X光tube可旋轉Ref.1XraytubeDetectorsGantryGantryApertureConventionalCTmachine-4thgenerationGantryAngulationApertureX-raytub

7、eTablemovementDetector180o90o270oRef.3GantryX-raytubeRotationStep-wisetablemovement1stscanlevel2ndscanlevel3rdscanlevelSlicesforconventionalCTRef.3InconventionalCT,aseriesofequallyspacedisrequiredsequentiallythroughaspecificregion,e.g.thehead.Thereisashortpauseaftereach

8、sectioninordertoadvancethepatienttabletothenextpresetposition.Thesectionthickness&overlap/intersectiongaparese